1. Field of the Invention
The present invention relates to a new species of microorganism and use for biocontrol of insect pests. More particularly, the invention relates to a newly discovered species of Chromobacterium bacterium that exhibits insecticidal activity. The invention also relates to metabolites obtained from the strain that possess insecticidal activity and to insecticidal compositions comprising cultures of the novel strain and/or supernatants, filtrates, and extracts obtained from the strain, and use thereof to control insect pests.
2. Description of the Art
Many insects, in particular leaf-feeding and sucking insects, are pestiferous and are responsible for substantial crop losses and reduced crop quality worldwide. Exemplary pestiferous leaf-feeding insects include insects of the order Coleoptera (beetles) such as the Colorado potato beetle and corn rootworm. Exemplary pestiferous leaf-feeding insects in the order Lepidoptera include diamondback moth and gypsy moth. Exemplary pestiferous sucking insects include insects of the Bemisia genus, in particular, Bemisia argentifolii Bellows & Perring (silverleaf whitefly).
The Colorado potato beetle (Chrysomelidae: Leptinotarsa decemlineata (Say)) is found throughout most of North America and is a major insect pest of potatoes, tomatoes, eggplant, and other solanaceous plants. Larvae and adults feed on the foliage of the host plants. Adult Colorado potato beetles overwinter in the soil and emerge in spring and establish themselves on a plant, mate, and the females lay clumps of eggs. Larvae hatch from the eggs in about 4 to 15 days, and the insect can go from egg to adult in as little as 21 days. Depending on the geographic location of the pest in North America, the Colorado potato beetle can complete one to three generations per year.
Control of the Colorado potato beetle is critical to prevent or reduce the substantial crop losses and reduced crop quality caused by this pest. Annual control of the Colorado potato beetle on potatoes, tomatoes, and eggplant is about $115 million. Of serious concern is the fact that the Colorado potato beetle has developed resistance to almost every chemical insecticide used against it and is showing signs of resistance to B. thuringiensis. The average of a chemical control agent in the field before resistance begins to develop is estimated to be 3.5 years. Additional means to control this pest are needed as well as an alternative to B. thuringiensis for organic producers.
The corn rootworm (Chrysomelidae: Diabrotica spp.) are leaf beetles that feed predominantly on corn. The larvae cause the most significant damage through feeding injury to the corn root. Adult corn rootworm beetles can also cause substantial foliar injury and interfere with pollination. Control of corn root worm is very expensive with some estimates reaching $1 billion. The Western corn rootworm (Dibrotica virgifera virgifera) has been cited as the most destructive pest of continuous corn in the United States today. Treatment expense and crop losses from the Western corn rootworm cost U.S. producers more than $1 billion annually. Additional control measures are needed to control this serious agricultural pest.
The diamondback moth (Lepidoptera: Plutellidae: Plutella xyostella L.) is one of the most widespread lepidopteran pests on vegetable brassica crops world wide, causing annual losses in the order of $1 billion. Host plants include virtually all cruciferous vegetable crops, including broccoli, cabbage, and cauliflower. Similar to the Colorado potato beetle, the diamondback moth is resistant to many pesticides, including, in some cases, B. thuringiensis. Alternative control, particularly organically based pesticides, is needed for this serious agricultural pest.
Whiteflies [Homoptera/Hemiptera] are found worldwide in tropical and subtropical areas as well as temperate zones. They are plant feeders, with piercing-sucking mouth parts that penetrate leaf tissue and puncture the plant leaf veins and withdraw plant sap. Economic losses and plant pest status occurs as a result of plant feeding and reduced crop yields, transmission of plant-infecting viruses, and product contamination from excreted honeydew. Whiteflies are characterized by high reproductive rates, logarithmic population growth, multiple plant hosts, and dispersal within and between plant hosts in response to plant senescence, wind, and other factors. Their habitats are found within and around field crops such as cotton and cultivated vegetables. There are at least 37 species identified in the Bemisia genus. Bemisia tabaci (Gennadius) (Homoptera/Hemiptera: Aleyrodidae) is one of the most serious economic pests attacking over 300 species of plants. The silverleaf whitefly, Bemisia argentifolii Bellows & Perring, is an even more serious pest, attacking as many as 500 different hosts. These include commercially grown crops as well as ornamentals and many alternative weed hosts. Recently, the silverleaf whitefly has also been reported to be present in greenhouses. In addition, the silverleaf whitefly is more prolific than B. tabaci. In the U.S., damage due to just one species of whitefly, the silverleaf whitefly, has been estimated at $500 million. Poinsettia is one of its favorite targets. According to the Nursery Men and Landscapers Association, the nursery and greenhouse industry in 1997 was a ten billion dollar industry. Because the silverleaf whitefly attacks commercially grown crops as well as ornamentals and many weed hosts, it is particularly difficult to control. For example, in the irrigated desert crop-growing areas of Arizona and California, sequential planting of cole crops, curcurbits, cotton, and alfalfa offers a continuum of year-round susceptible host material and the opportunity for whiteflies to move within and among cropping systems to expand population development. Whiteflies are difficult to control with insecticides, and have developed resistance to some pesticides. Therefore, additional control methods for whiteflies are needed.
Biological control agents (biopesticides) can be an important addition or alternative to control using synthetic chemical pesticides and important in integrated pest management. Many factors are involved in a successful microbial control agent, including survival in the environment, mode of entry in the gut, and replication in the insect. Although some microbes (e.g., Bacillus thuringiensis Berliner) kill by toxins, the replicating organism also contributes to the overall control of the insect (Schnepf et al. 1998).
Strains of bacterial species that kill insects have been reported. Paenibacillus popilliae was the first bacterial pesticide (Milky Spore) to successfully control pest insects (Japanese beetles; Dutky, 1940). Various strains of B. thuringiensis are toxic to other scarab beetles (Ohba et al., 1992), Diabrotica spp. (Tailor et al., 1992), caterpillars, beetles, and mosquitoes (Schnepf et al., 1998). Bacillus thuringiensis has been used for control of the Colorado potato beetle as a foliar spray (Ferro et al., 1997) or in transgenic plants (Perlak et al., 1993). Heins et al., U.S. Pat. Nos. 6,417,163 and 6,291,426, report compositions and methods for controlling plant pests including the Colorado potato beetle using a novel strain of Bacillus subtilis, AQ713. Serratia entomophila and Serratia proteamaculans (Jackson et al., 1993) cause amber disease in grass grubs and are being developed in New Zealand. Photorhabdus luminescens, with nematodes as a vector, has been described as pathogenic to Lepidoptera (Forst and Nealson, 1996). High molecular weight protein complexes isolated from P. luminescens are toxic to lepidopteran and coleopteran insects (Bowen et al., 1998; Guo et al., 1999). One of these complexes, Tca, has been shown to disrupt the midgut epithelium of tobacco hornworm larvae (Blackburn et al., 1998).
Many bacterial insect pathogens are not toxic enough for field control. Other than B. thuringiensis as discussed above, few other bacteria have been used to effectively control Colorado potato beetles (Onstad, 2001). Pathogens such as Serratia marcescens Bizo (Grimont & Grimont, 1978) or Spiroplasma leptinotarsae Hackett et al. (Hackett et al., 1996) while causing mortality of beetles in the lab, do not effectively control this pest in the field.
Successful fungal biocontrol agents for the Colorado potato beetle pest include Beauveria bassiana which has been the most successful in some areas such as Europe and the northern United States and under certain conditions such as early season applications in Virginia requiring high humidity and low temperatures (Groden and Lockwood, 1991; Poprawski et al., 1997; Martin et al., 1999).
Purple bacteria (Chromobacterium violaceum) have infrequently been isolated from insects, and have not been previously considered an insect pathogen (Bucher, 1981). This species of bacteria has been isolated from the digestive tract of the larger grain borer (Prostephanus truncatus) where they may be involved in cellulose digestion in this insect (Vazquez-Artista et al., 1997) forming a symbiotic rather than a pathogenic association. However, C. violaceum is mainly known for its production of a purple pigment, violacein, which has anti-microbial activity against Gram-positive and Gram-negative bacteria (Duran et al., 1983) and Trypanosoma cruzi (Duran et al., 1994).